1. Field of the Invention
The present invention relates to an apparatus for measuring impurities in water, and more particularly to an apparatus for measuring solids content of water indirectly based on the time dependent change of the flow rate of water passing through a pair of filters having different pore sizes.
2. Description of the Prior Art
Conventionally, a direct microscopic method, FI (Fourier Index) value method (disclosed as SDI method in Handoutai Process Zairyo Jitsumu Binran p. 438 published by Science Forum Company, Apr. 25, 1983) and the like have been known as methods for evaluating the quality of pure water. According to the first mentioned method, pure water passes through a filter of 0.2 .mu.m pore hole diameter and minute particles on the filter are examined with a microscope. According to the second mentioned method, a prescribed amount of pure water passes through a filter of 0.45 .mu.m pore hole diameter under a constant pressure and the passing through time is measured.
It is known that among impurities in water there are materials having extremely small particle diameters such as colloidal materials. However, in the above described direct microscopic method, only particles larger than 0.2 .mu.m can be captured, so that the aforementioned colloidal materials can not be measured. In addition, much labor and skill are required in the measurement. In the FI value method, only a filter having a pore diameter larger than 0.45 .mu.m is used at present in consideration of the time required for filtering. Accordingly, in the FI value method, only minute particles larger than 0.45 .mu.m can be captured, so that the aforementioned colloidal materials can not be measured. In addition, neither of the above described methods is capable of continuous monitoring in the field where the water is used so that neither can cope with a sudden change in the quality of water.